This specification relates generally to the detection of a weather hazard in the atmosphere. More particularly, this specification relates to weather hazard detection using aircraft equipment.
Hazardous weather is generally associated with weather cells or storms. Weather cells such as convective weather cells include moisture and can produce turbulence, high winds, lightning, hail, and other weather hazards. A measure of the extent of a given weather hazard to an aircraft in flight is vertically integrated liquid (VIL) content. VIL content is a parameter that indicates the estimated amount of water in a column of air extending from the ground upwards. VIL content is measured in units of kg of water per m2. The Federal Meteorological Handbook volume on weather radar generally refers to VIL as “vertically integrated liquid water” and provides an algorithm that is used to display VIL values as an image. The output of the VIL algorithm can be used to produce the product that is updated once per volume scan. Federal Aviation Agency (FAA) guidelines restrict air travel in regions where the estimate of VIL content is greater than 3.5 kg/m2.
Conventional estimations of the VIL content in a given location are provided by the National Weather Service (NWS). For example, the NWS can provide VIL content based upon data from the NEXRAD network of weather radar installations. For aircraft, the VIL content estimates are generally transmitted from the NWS via a radio communications link while the aircraft is in flight or provided to the flight crew while on the ground. Since the NWS VIL content estimates can be computed at a maximum frequency of 1 estimate per 4 minute interval (the maximum scan rotation rate of a NEXRAD radar installation), the data may be stale (5 to 15 minutes old) by the time it reaches a flight crew. The algorithm used by the NWS to calculate VIL content is described in a paper by Douglas R. Greene of NOAA and Robert A. Clark of Texas A&M University entitled, “Vertically Integrated Liquid Water—A New Analysis Tool,” (Monthly Weather Review, Vol. 100, No. 7, pp. 548 ff. 1972). The formula derived for calculating VIL content using a continuous sampling of reflectivity from the base of a storm to the top of the storm is:M*=∫hbasehtopMdh′=3.44×10−6∫hbasehtopZ4/7dh′                where Z is the radar reflectivity;        M* is the mass of raindrops per unit area (summing all altitudes);        hTop is the altitude of the top of the storm;        hBase is the altitude of the bottom of the storm; and        M is the mass of raindrops per unit volume (x·y·dh).        
Conventional systems apply a discrete version of this formula, adding the maximum reflectivity within each volume element defined around the 1-degree beams of the radar. Since the scan patterns often space the beams at more than 1-degree increments vertically, extrapolation of the reflectivity value across a greater vertical range is often required.
Conventional aircraft hazard weather radar systems, such as the WXR 2100 MultiScan™ radar system manufactured by Rockwell Collins, Inc., have Doppler capabilities and are capable of detecting at least four parameters: weather range, weather reflectivity, weather velocity, and weather spectral width or velocity variation. The weather reflectivity is typically scaled to green, yellow, and red color levels that are related to rainfall rate. The radar-detected radial velocity variation can be scaled to a turbulence level and displayed as magenta. Such weather radar systems can conduct vertical sweeps and obtain reflectivity parameters at various altitudes.
Due to constraints on antenna size, the airborne weather radar often has a broader beam than the NEXRAD installations. The airborne weather radar system also favors update speed over scan completeness, so only two elevations are sampled in certain multi-scanning modes. In certain conventional systems, the elevations are nominally targeted at the freezing level and the higher −40° C. level of the atmosphere as returns at these levels are strong indicators of storm severity. Heretofore, airborne weather radar systems have not calculated VIL content from weather radar returns received by airborne weather radars.
Thus, there is a need for an aircraft hazard warning system method that provides VIL content detection. There is also a need for a hazard detection system that uses on-board aircraft detected VIL content parameters. There is also a need for a VIL content detection system and method that does not require a NEXRAD system. Further still, there is a need for a VIL content detection system that does not add significant cost or weight to an aircraft weather radar system. Yet further, there is a need for an aircraft hazard warning system having a radar scan optimized to determine the VIL content from a small number of reflectivity samples. Further, there is a need for a system and method of more timely and more accurate detection of VIL content parameters.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.